Physical quantity sensor, pressure sensor, altimeter, electronic apparatus, and moving object

ABSTRACT

A physical quantity sensor includes a semiconductor substrate, a diaphragm section that is disposed on the semiconductor substrate and is flexurally deformed when receiving pressure, a sensor element that is disposed on the diaphragm section, an element-periphery structure member that is disposed on one surface side of the semiconductor substrate and forms a cavity section together with the diaphragm section, and a semiconductor circuit that is provided on the same surface side as the element-periphery structure member of the semiconductor substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation patent application of U.S. application Ser. No.14/573,537 filed Dec. 17, 2014, which claims priority to Japanese PatentApplication No. 2013-261887, filed Dec. 18, 2013 is expresslyincorporated by reference herein in their entireties.

BACKGROUND

1. Technical Field

The present invention relates to a physical quantity sensor, a pressuresensor, an altimeter, an electronic apparatus, and a moving object.

2. Related Art

A pressure sensor that includes a diaphragm which is flexurally deformedwhen receiving pressure is widely used. In such a pressure sensor, asensor element such as a piezoresistive element or a vibration elementis disposed on the diaphragm, then the sensor element detects theflexure of the diaphragm, and thus it is possible to detect pressureapplied to the diaphragm.

For example, in a pressure sensor disclosed in JP-A-8-97439, apiezoresistive element and an integrated circuit (IC) that includes acircuit for drive, detection, or the like of the piezoresistive elementare provided on one surface of a silicon substrate on which a diaphragmis formed, and a cavity is provided on the other surface of the siliconsubstrate. The cavity is sealed, and thereby it is possible to realizean absolute-pressure sensor.

However, in the pressure sensor disclosed in JP-A-8-97439, since thecavity is provided on a side opposite to the integrated circuit of thesilicon substrate, a problem arises in that the size of the siliconsubstrate becomes great in the thickness direction. In addition, in thepressure sensor disclosed in JP-A-8-97439, in a case where the sealedcavity is formed, a process has to be included, in which anothersubstrate is bonded to the silicon substrate. Therefore, a problemarises in that cost has to be increased.

SUMMARY

An advantage of some aspects of the invention is to provide a physicalquantity sensor, in which it is possible to achieve a low profile and tolower cost, and in addition, to provide a pressure sensor, an altimeter,an electronic apparatus, and a moving object which include the physicalquantity sensor.

Application Example 1

This application example is directed to a physical quantity sensorincluding: a semiconductor substrate; a diaphragm section that isdisposed on the semiconductor substrate and is flexurally deformed whenreceiving pressure; a sensor element that is disposed on the diaphragmsection; a wall section that is disposed on one surface side of thesemiconductor substrate and configures a cavity together with thediaphragm section; and a circuit section that is provided on the samesurface side as the wall section of the semiconductor substrate.

With this configuration, since the cavity (or wall section) and thecircuit section are provided on the same surface side of thesemiconductor substrate, a structure member that forms the cavity doesnot stick out from the side opposite to the circuit section of thesemiconductor substrate. Therefore, it is possible to achieve a lowprofile. In addition, a CMOS process (particularly a process of formingan inter-layer insulation film or a wiring layer) is used, and it ispossible to collectively form the wall section with the circuit section.Therefore, a manufacturing process of the physical quantity sensor issimplified, and as a result, it is possible to lower the cost of thephysical quantity sensor. In addition, even in a case where the cavityis sealed, it is possible to seal the cavity using a film formationmethod, and thus there is no need to bond substrates so as to seal thecavity as in the related art. In this way, the manufacturing process ofthe physical quantity sensor is also simplified, and as a result, it ispossible to lower the cost of the physical quantity sensor.

Application Example 2

In the physical quantity sensor according to the application example ofthe invention, it is preferable that the sensor element has apiezoresistive element.

With this configuration, in a case where the piezoresistive element andthe circuit section are disposed on the same surface side of thesemiconductor substrate, the CMOS process (particularly a process offorming a transistor) is used, and it is possible to collectively formthe piezoresistive element with the circuit section. Therefore, it ispossible to further simplify the manufacturing process of the physicalquantity sensor.

Application Example 3

In the physical quantity sensor according to the application example ofthe invention, it is preferable that the sensor element is disposed onthe same surface side as the wall section of the diaphragm section.

With this configuration, a CMOS process (particularly a process offorming a transistor) is used, and it is possible to collectively formthe sensor element with the circuit section. Therefore, it is possibleto further simplify the manufacturing process of the physical quantitysensor. In addition, it is possible to accommodate the sensor elementinside the cavity, and therefore, it is possible to prevent the sensorelement from degrading or to decrease characteristic degradation of thesensor element.

Application Example 4

In the physical quantity sensor according to the application example ofthe invention, it is preferable that the circuit section has aninsulation layer that is disposed on the semiconductor substrate and awiring section that penetrates through the insulation layer, and thatthe wall section is formed through the same film formation as at leastone of the insulation layer and the wiring section.

With this configuration, the CMOS process (particularly a process offorming an inter-layer insulation film or a wiring layer) is used, andit is possible to collectively form the wall section with the circuitsection.

Application Example 5

In the physical quantity sensor according to the application example ofthe invention, it is preferable that the diaphragm section includes alayer that is configured of a material which has a lower etching ratewith respect to an acid etchant than the insulation layer.

With this configuration, when an insulation layer formed integrally withthe insulation layer that is included in the circuit section is etchedby using the acid etchant and forms the cavity (wall section), it ispossible to use such a layer as an etching stop layer. Therefore, it ispossible to efficiently form the diaphragm section having a desiredthickness.

Application Example 6

In the physical quantity sensor according to the application example ofthe invention, it is preferable that the diaphragm section includes alayer that is configured of a material which has a lower etching ratewith respect to an alkali etchant than the semiconductor substrate.

With this configuration, when the semiconductor substrate is etched byusing the alkali etchant from the side opposite to the wall section andforms the diaphragm section, it is possible to use such a layer as anetching stop layer. Therefore, it is possible to efficiently form thediaphragm section having a desired thickness.

Application Example 7

In the physical quantity sensor according to the application example ofthe invention, it is preferable that the diaphragm section includes atleast one film of a silicon oxide film, a silicon nitride film, and ametal film.

With this configuration, the insulation layer that is included in thecircuit section is generally configured of the silicon oxide film, butthe silicon nitride film has a lower etching rate with respect to theacid etchant than the silicon oxide film. Thus, when an insulation layerformed integrally with the insulation layer that is included in thecircuit section is etched by using the acid etchant and forms the cavity(wall section), it is possible to use the silicon nitride film as anetching stop layer.

In addition, the silicon oxide film, the silicon nitride film, and themetal film all have a lower etching rate with respect to the alkalietchant than silicon. Thus, when the silicon substrate (semiconductorsubstrate) is etched by using the alkali etchant from the side oppositeto the wall section, and forms the diaphragm section, it is possible touse these films as the etching stop layer.

In addition, the silicon oxide film and the silicon nitride film haverelatively high insulation properties. Thus, the sensor element isdisposed on these films, and therefore it is possible to prevent a shortcircuit of the wiring drawn out from each section of the sensor elementor the sensor element.

Application Example 8

In the physical quantity sensor according to the application example ofthe invention, it is preferable that the inside of the cavity isdepressurized to be below atmospheric pressure.

With this configuration, it is possible to use the physical quantitysensor as a so-called absolute pressure sensor.

Application Example 9

This application example is directed to a pressure sensor including: thephysical quantity sensor according to the application examples of theinvention.

With this configuration, it is possible to provide a pressure sensorthat includes the physical quantity sensor which is intended to achievea low profile and to lower cost.

Application Example 10

This application example is directed to an altimeter including: thephysical quantity sensor according to the application examples of theinvention.

With this configuration, it is possible to provide an altimeter thatincludes the physical quantity sensor which is intended to achieve a lowprofile and to lower cost.

Application Example 11

This application example is directed to an electronic apparatusincluding: the physical quantity sensor according to the applicationexamples of the invention.

With this configuration, it is possible to provide an electronicapparatus that includes the physical quantity sensor which is intendedto achieve a low profile and to lower cost.

Application Example 12

This application example is directed to a moving object including: thephysical quantity sensor according to the application examples of theinvention.

With this configuration, it is possible to provide a moving object thatincludes the physical quantity sensor which is intended to achieve a lowprofile and to lower cost.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a cross-sectional view illustrating a first embodiment of aphysical quantity sensor according to the invention.

FIG. 2 is an enlarged plan view of a diaphragm section and a portion inthe vicinity of the diaphragm section of the physical quantity sensorillustrated in FIG. 1.

FIG. 3 is a view illustrating a bridge circuit that includes a sensorelement (piezoresistive element) that is included in the physicalquantity sensor illustrated in FIG. 1.

FIGS. 4A and 4B are views for illustrating an operation of the physicalquantity sensor illustrated in FIG. 1. FIG. 4A is a cross-sectional viewillustrating a pressurized state, and FIG. 4B is a plan viewillustrating the pressurized state.

FIGS. 5A to 5D are views illustrating a manufacturing process of thephysical quantity sensor illustrated in FIG. 1.

FIGS. 6A to 6D are views illustrating the manufacturing process of thephysical quantity sensor illustrated in FIG. 1.

FIG. 7 is a cross-sectional view illustrating a second embodiment of aphysical quantity sensor according to the invention.

FIG. 8 is a cross-sectional view illustrating a third embodiment of aphysical quantity sensor according to the invention.

FIG. 9 is a cross-sectional view illustrating an example of a pressuresensor according to the invention.

FIG. 10 is a perspective view illustrating an example of an altimeteraccording to the invention.

FIG. 11 is a front view illustrating an example of an electronicapparatus according to the invention.

FIG. 12 is a perspective view illustrating an example of a moving objectaccording to the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, a physical quantity sensor, a pressure sensor, analtimeter, an electronic apparatus, and a moving object according to theinvention will be described in detail in accordance with each embodimentillustrated in the accompanying drawings.

First Embodiment 1. Physical Quantity Sensor

FIG. 1 is a cross-sectional view illustrating a first embodiment of thephysical quantity sensor according to the invention. FIG. 2 is anenlarged plan view of a diaphragm section and a portion in the vicinityof the diaphragm section of the physical quantity sensor illustrated inFIG. 1. FIG. 3 is a view illustrating a bridge circuit that includes asensor element (piezoresistive element) that is included in the physicalquantity sensor illustrated in FIG. 1. In addition, FIGS. 4A and 4B areviews for illustrating an operation of the physical quantity sensorillustrated in FIG. 1. FIG. 4A is a cross-sectional view illustrating apressurized state, and FIG. 4B is a plan view illustrating thepressurized state.

A physical quantity sensor 1 illustrated in FIG. 1 includes a substrate6, a sensor element 7, an element-periphery structure member 8, a cavitysection 5 (cavity), and a semiconductor circuit 9 (circuit section).Each of the above members is described in the above order.

Substrate 6

The substrate 6 has a plate-like shape, and is configured to have asemiconductor substrate 61 that is configured of a semiconductor such assilicon, a silicon oxide film 62 that is provided on one surface of thesemiconductor substrate 61, and a silicon nitride film 63 that isprovided on the silicon oxide film 62. The shape of such a substrate 6in a plan view is not limited and, for example, can be a quadrilateralsuch as substantially a square or substantially a rectangle or a circle.Here, the silicon oxide film 62 and the silicon nitride film 63 can bothbe used as an insulation film.

In addition, a diaphragm section 64 that is formed to be thinner thanthe periphery and flexurally deformed when receiving pressure isprovided on the substrate 6. The diaphragm section 64 is formed to havea bottomed concave section 65 provided on the underside of the substrate6. The underside of such a diaphragm section 64 has a pressure receivingsurface 641. As illustrated in FIG. 2, the diaphragm section 64 is asquare in a plan view.

The diaphragm section 64 is disposed on the semiconductor substrate 61.In the substrate 6 according to the present embodiment, the concavesection 65 penetrates the semiconductor substrate 61, and the diaphragmsection 64 is configured to have two layers of the silicon oxide film 62and the silicon nitride film 63. Such a diaphragm section 64 may beextremely thin. Therefore, the physical quantity sensor 1 has extremelyhigh sensitivity. In addition, these films can be used as an etchingstop layer when manufacturing the physical quantity sensor 1, as will bedescribed later, and it is possible to decrease variations in thethickness of the diaphragm section 64 for each product.

The concave section 65 does not penetrate the semiconductor substrate61, and the diaphragm section 64 may be configured to have three layersof a thin portion of the semiconductor substrate 61, the silicon oxidefilm 62, and the silicon nitride film 63.

Sensor Element 7

The sensor element 7 is configured to have a plurality (four in theembodiment) of piezoresistive elements 7 a, 7 b, 7 c, and 7 d which isprovided on the diaphragm section 64 of the substrate 6, as illustratedin FIG. 2.

The piezoresistive elements 7 a and 7 b are provided to correspond toone pair of opposite (parallel in a horizontal direction in FIG. 2)sides (hereinafter, also referred to as “first sides”) of the diaphragmsection 64 that is a quadrilateral in a plan view. The piezoresistiveelements 7 c and 7 d are provided to correspond to the other pair ofopposite (parallel in a vertical direction in FIG. 2) sides(hereinafter, also referred to as “second sides”) of the diaphragmsection 64 that is a quadrilateral in a plan view.

The piezoresistive element 7 a has a piezoresistive portion 71 aprovided in the vicinity of the outer circumference of the diaphragmsection 64 (more specifically, in the vicinity of a first side on theright side in FIG. 2). The piezoresistive portion 71 a has alongitudinal shape extending along a direction parallel to the firstsides. Wirings 41 a are connected to the opposite ends of thepiezoresistive portion 71 a, respectively.

Similarly, the piezoresistive element 7 b has a piezoresistive portion71 b provided in the vicinity of the outer circumference of thediaphragm section 64 (more specifically, in the vicinity of a first sideon the left side in FIG. 2). Wirings 41 b are connected to the oppositeends of the piezoresistive portion 71 b, respectively.

Meanwhile, the piezoresistive element 7 c has a pair of piezoresistiveportions 71 c provided in the vicinity of the outer circumference of thediaphragm section 64 (more specifically, in the vicinity of a secondside on the upper side in FIG. 2) and a connection portion 73 c thatconnects the pair of piezoresistive portions 71 c to each other. Thepair of piezoresistive portions 71 c is parallel to each other, and hasa longitudinal shape extending along a direction perpendicular to thesecond sides (that is, a direction parallel to the first sides). Ends onone side of the pair of piezoresistive portions 71 c (ends on the centerside of the diaphragm section 64) are connected to each other throughthe connection portion 73 c, and wirings 41 c are connected to ends onthe other side of the pair of piezoresistive portions 71 c (ends on theouter circumferential side of the diaphragm section 64), respectively.

Similarly, the piezoresistive element 7 d has a pair of piezoresistiveportions 71 d provided in the vicinity of the outer circumference of thediaphragm section 64 (more specifically, in the vicinity of a secondside on the lower side in FIG. 2) and a connection portion 73 d thatconnects the pair of piezoresistive portions 71 d to each other. Ends onone side of the pair of piezoresistive portions 71 d (ends on the centerside of the diaphragm section 64) are connected to each other throughthe connection portion 73 d, and wirings 41 d are connected to ends onthe other side of the pair of piezoresistive portions 71 d (ends on theouter circumferential side of the diaphragm section 64), respectively.

The piezoresistive portions 71 a, 71 b, 71 c, and 71 d of suchpiezoresistive elements 7 a, 7 b, 7 c, and 7 d are each configured ofpolysilicon (polycrystalline silicon) doped (dispersed or implanted)with impurities such as phosphorus or boron. In addition, the connectionportions 73 c and 73 d of the piezoresistive elements 7 c and 7 d andthe wirings 41 a, 41 b, 41 c, and 41 d are configured of polysilicon(polycrystalline silicon) doped (dispersed or implanted) with impuritiessuch as phosphorus or boron at a higher concentration than in thepiezoresistive portions 71 a, 71 b, 71 c, and 71 d. The connectionportions 73 c and 73 d and the wirings 41 a, 41 b, 41 c, and 41 d may beconfigured of a metal.

In addition, the piezoresistive elements 7 a, 7 b, 7 c, and 7 d areconfigured so as to have equal resistance values to each other intheory. The piezoresistive elements 7 a, 7 b, 7 c, and 7 d areelectrically connected to each other through the wirings 41 a, 41 b, 41c, and 41 d, and configure a bridge circuit 70 (Wheatstone bridgecircuit) as illustrated in FIGS. 4A and 4B. A drive circuit (notillustrated) that supplies a drive voltage AVDC is connected to thebridge circuit 70. The bridge circuit 70 outputs a signal (voltage) inaccordance with the resistance values of the piezoresistive elements 7a, 7 b, 7 c, and 7 d.

In addition, even though such a sensor element 7 uses an extremely thindiaphragm section 64 as described above, there is no problem occurringin which a Q value decreases due to vibration leakage to the diaphragmsection 64 unlike in a case where a vibration element such as aresonator is used as the sensor element.

Element-Periphery Structure Member 8

The element-periphery structure member 8 is formed to partition thecavity section 5 in which the sensor element 7 is disposed. Here, theelement-periphery structure member 8 is disposed on one surface side ofthe semiconductor substrate 61 and configures a “wall section” thatforms a cavity section 5 together with the diaphragm section 64.

The element-periphery structure member 8 includes an inter-layerinsulation film 81 formed so as to surround the sensor element 7 on thesubstrate 6, a wiring layer 82 formed on the inter-layer insulation film81, an inter-layer insulation film 83 formed on the wiring layer 82 andthe inter-layer insulation film 81, a wiring layer 84 that is formed onthe inter-layer insulation film 83 and has a covering layer 841 in whicha plurality of fine holes (open holes) is provided, a front surfaceprotective film 85 formed on the wiring layer 84 and the inter-layerinsulation film 83, and a sealing layer 86 provided on the coveringlayer 841. Here, the wiring layers 82 and 84 include wiring layers 82 aand 84 a which are formed so as to surround the cavity section 5, andwiring layers 82 b and 84 b which configure the wiring of thesemiconductor circuit 9. In addition, a layer 42 is provided between thewiring layer 82 a and the silicon nitride film 63. The layer 42 isformed collectively with the sensor element 7 as will be describedlater, but may not be provided. In addition, a part of the inter-layerinsulation film 81 is interposed between the wiring layer 82 a and thesilicon nitride film 63, which is not illustrated.

The semiconductor circuit 9 is fabricated on and above the semiconductorsubstrate 61. Thus, the semiconductor circuit 9 is provided on the samesurface side as the element-periphery structure member 8 of thesemiconductor substrate 61. The semiconductor circuit 9 includes anactive element such as a MOS transistor 87, and other circuit componentssuch as a capacitor, an inductor, a resistor, a diode, and a wiring(including the wiring that is connected to the sensor element 7 andwiring layers 82 b and 84 b) which are formed, as necessary. Here, theMOS transistor 87 includes a source and a drain (not illustrated) whichare doped with impurities such as phosphorus or boron and formed on thetop surface of the semiconductor substrate 61, a gate insulation film(not illustrated) formed on a channel region that is formed between thesource and the drain, and a gate electrode 871 formed on the gateinsulation film.

Cavity Section 5

The cavity section 5 partitioned by the substrate 6 and theelement-periphery structure member 8 functions as an accommodationsection in which the sensor element 7 is accommodated. In addition, thecavity section 5 is a sealed space. The cavity section 5 functions as apressure reference chamber to provide a reference value of pressuredetected by the physical quantity sensor 1. According to the embodiment,the cavity section 5 is in a vacuum state (300 Pa or lower). The cavitysection 5 is in the vacuum state, and therefore it is possible to usethe physical quantity sensor 1 as an “absolute pressure sensor” thatdetects pressure with the vacuum state as a reference, and thus itsconvenience is improved.

However, the cavity section 5 may not have the vacuum state, but insteadmay be at atmospheric pressure, a depressurized state in which airpressure is lower than atmospheric pressure, or a pressurized state inwhich air pressure is higher than atmospheric pressure. In addition, aninert gas such as a nitrogen gas or a rare gas may be sealed in thecavity section 5.

As above, the configuration of the physical quantity sensor 1 has beenconcisely described.

In the physical quantity sensor 1 having such a configuration, thediaphragm section 64 is deformed in accordance with the pressure that isreceived by the pressure receiving surface 641 of the diaphragm section64 as illustrated in FIG. 4A, therefore the piezoresistive elements 7 a,7 b, 7 c, and 7 d are strained as illustrated in FIG. 4B, and theresistance values of the piezoresistive elements 7 a, 7 b, 7 c, and 7 dare changed. Accordingly, an output of the bridge circuit 70 (see FIG.3) that is configured to have the piezoresistive elements 7 a, 7 b, 7 c,and 7 d is changed, and thus it is possible to obtain the magnitude ofthe pressure received by the pressure receiving surface 641 based on theoutput.

To be more specific, since the resistance values of the piezoresistiveelements 7 a, 7 b, 7 c, and 7 d are equal to each other as describedabove, the product of the resistance values of the piezoresistiveelements 7 a and 7 b is equal to the product of the resistance values ofthe piezoresistive elements 7 c and 7 d in theory before the diaphragmsection 64 is deformed as described above, and thus the output(potential difference) of the bridge circuit 70 should be zero.

Meanwhile, when the diaphragm section 64 is deformed as described aboveas illustrated in FIG. 4B, the piezoresistive portions 71 a and 71 b ofthe piezoresistive elements 7 a and 7 b are subjected to a tensilestrain along the longitudinal direction thereof and to a compressionstrain along the width direction thereof, and simultaneously thepiezoresistive portions 71 c and 71 d of the piezoresistive elements 7 cand 7 d are subjected to a compression strain along the longitudinaldirection thereof and to a tensile strain along the width directionthereof.

Here, the deformation of the diaphragm section 64 as described abovecauses the piezoresistive portions 71 a and 71 b to receive thecompression force in the width direction thereof, but the piezoresistiveportions 71 a and 71 b are subjected to the tensile strain along thelongitudinal direction thereof in accordance with Poisson's ratio of thepiezoresistive portions 71 a and 71 b. In addition, the deformation ofthe diaphragm section 64 as described above causes the piezoresistiveportions 71 c and 71 d to receive the compression force in thelongitudinal direction thereof, and the piezoresistive portions 71 c and71 d are subjected to the compression strain along the longitudinaldirection thereof in accordance with the compression force.

The strain of the piezoresistive portions 71 a, 71 b, 71 c, and 71 dcauses a difference to occur between the product of resistance values ofthe piezoresistive elements 7 a and 7 b and the product of resistancevalues of the piezoresistive elements 7 c and 7 d, and an output(potential difference) in accordance with the difference is output fromthe bridge circuit 70. It is possible to obtain the magnitude (absolutepressure) of the pressure received by the pressure receiving surface 641based on the output from the bridge circuit 70.

Here, when the diaphragm section 64 is deformed as described above, theresistance values of the piezoresistive elements 7 a and 7 b areincreased and the resistance values of the piezoresistive elements 7 cand 7 d are decreased. Therefore, it is possible to significantly changethe difference between the product of the resistance values of thepiezoresistive elements 7 a and 7 b and the product of the resistancevalues of the piezoresistive elements 7 c and 7 d, and thus it ispossible to increase the output from the bridge circuit 70. As a result,it is possible to increase pressure detection sensitivity. In addition,since all of the piezoresistive elements 7 a, 7 b, 7 c, and 7 d thatconfigure the bridge circuit 70 have substantially the same temperaturesensitivity, it is possible to decrease characteristic changes dependingon an external temperature change.

In the physical quantity sensor 1 as described above, the cavity section5 and the semiconductor circuit 9 are provided on the same surface sideof the semiconductor substrate 61. Therefore, the element-peripherystructure member 8 that forms the cavity section 5 does not stick outfrom the side opposite to the semiconductor circuit 9 of thesemiconductor substrate 61, and thus it is possible to achieve a lowprofile. Thus, the element-periphery structure member 8 is formedthrough the same film formation as at least one of the inter-layerinsulation films 81 and 83 and the wiring layers 82 and 84. Accordingly,the CMOS process (particularly a process of forming the inter-layerinsulation films 81 and 83 and the wiring layers 82 and 84) is used, andit is possible to collectively form the element-periphery structuremember 8 with the semiconductor circuit 9. Therefore, the manufacturingprocess of the physical quantity sensor 1 is simplified, and as aresult, it is possible to lower cost of the physical quantity sensor 1.In addition, even in a case where the cavity section 5 is sealed as inthe embodiment, it is possible to seal the cavity section 5 using a filmformation method and thus there is no need to bond substrates so as toseal the cavity as in the related art. In this point, the manufacturingprocess of the physical quantity sensor 1 is simplified, and as aresult, it is possible to lower the cost of the physical quantity sensor1.

In addition, the sensor element 7 includes the piezoresistive elements 7a, 7 b, 7 c, and 7 d as described above, and the sensor element 7 andthe semiconductor circuit 9 are disposed on the same surface side of thesemiconductor substrate 61. Therefore, the CMOS process (particularly, aprocess of forming the transistor 87) is used, and it is possible tocollectively form the sensor element 7 with the semiconductor circuit 9.Therefore, in this point, it is possible to further simplify themanufacturing process of the physical quantity sensor 1.

In addition, since the sensor element 7 is disposed on theelement-periphery structure member 8 side of the diaphragm section 64,it is possible to accommodate the sensor element 7 inside the cavitysection 5, and thus it is possible to prevent the sensor element 7 fromdegrading or in other words to decrease the characteristic degradationof the sensor element 7.

In addition, the diaphragm section 64 includes the silicon nitride film63 as a layer that is configured of a material which has a lower etchingrate with respect to an acid etchant than the inter-layer insulationfilms 81 and 83.

In general, the inter-layer insulation films 81 and 83 included in thesemiconductor circuit 9 are configured to have the silicon oxide film,however, the silicon nitride film has a lower etching rate with respectto the acid etchant than the silicon oxide film. Accordingly, when aninsulation layer formed integrally with the inter-layer insulation films81 and 83 that are included in the semiconductor circuit 9 is etched byusing the acid etchant and forms the cavity section 5 (element-peripherystructure member 8), it is possible to use such a layer (silicon nitridefilm 63) as an etching stop layer. Therefore, it is possible toefficiently form the diaphragm section 64 having a desired thickness.

In addition, the diaphragm section 64 includes the silicon oxide film 62and the silicon nitride film 63 as layers that are configured ofmaterials that have a lower etching rate with respect to an alkalietchant than the semiconductor substrate 61.

Accordingly, the silicon oxide film 62 and the silicon nitride film 63all have a lower etching rate with respect to the alkali etchant thansilicon. Thus, when the semiconductor substrate 61 is etched by usingthe alkali etchant from the side opposite to the element-peripherystructure member 8, and forms the diaphragm section 64, it is possibleto use these layers (silicon oxide film 62 according to the embodiment)as the etching stop layer. Therefore, in this point, it is possible toefficiently form the diaphragm section 64 having the desired thickness.

In addition, the silicon oxide film 62 and the silicon nitride film 63have relatively high insulation properties. Thus, the sensor element 7is disposed on these films (silicon nitride film 63 according to theembodiment), and thus it is possible to prevent a short circuit of thewiring drawn out from each section of the sensor element 7 or the sensorelement 7.

Next, a manufacturing method of the physical quantity sensor 1 will bedescribed concisely.

FIGS. 5A to 6D are views illustrating the manufacturing process of thephysical quantity sensor illustrated in FIG. 1. Hereinafter, descriptionis provided with reference to these drawings.

Sensor Element•MOS Transistor Forming Processes

First, as illustrated in FIG. 5A, the top surface of the semiconductorsubstrate 61A such as a silicon substrate is thermally oxidized suchthat the silicon oxide film 62 is formed, and further, the siliconnitride film 63 is formed on the silicon oxide film 62 by using asputtering method, a CVD method, or the like. Accordingly, a structuremember 10 is obtained.

The silicon oxide film 62 functions as an inter-element separating filmwhen the semiconductor circuit 9 is formed on and above thesemiconductor substrate 61. In addition, the silicon nitride film 63 hasresistance to etching in a cavity section forming process which will beperformed later, and functions as an etching stop layer. The siliconnitride film 63 is formed to be restricted in a range including a planerange in which the sensor element 7 is formed and a range of a part ofelement (capacitor) or the like in the semiconductor circuit 9, by apatterning process. Accordingly, there is no obstruction encounteredwhen the semiconductor circuit 9 is formed on and above thesemiconductor substrate 61.

In addition, the gate insulation film of the MOS transistor 87 is formedby thermal-oxidation and the source and drain of the MOS transistor 87of the semiconductor circuit 9 is formed by being doped with impuritiessuch as phosphorus or boron on a portion on the top surface of thesemiconductor substrate 61A, where the silicon oxide film 62 and thesilicon nitride film 63 are not formed (not illustrated).

Next, a polycrystalline silicon film (or amorphous silicon film) isformed on the top surface of the structure member 10 by using thesputtering method, the CVD method, or the like, the polycrystallinesilicon film is patterned by etching, and an element forming film 7A,the layer 42, and the gate electrode 871 for forming the sensor element7 are formed as illustrated in FIG. 5B. Accordingly, a structure member10A including the element forming film 7A and the MOS transistor 87 isobtained.

Here, a thickness of the polycrystalline silicon film is notparticularly limited, but, for example, is about 200 nm to 400 nm.

Next, after a photoresist film 20 is formed on a part of the top surfaceof the structure member 10A so as to expose the element forming film 7A,impurities such as phosphorus or boron dope (are ion-implanted on) theelement forming film 7A, and then the sensor element 7 is formed asillustrated in FIG. 5C. Accordingly, a structure member 10B includingthe sensor element 7 and the MOS transistor 87 is obtained.

During the ion implantation, the shape of the photoresist film 20, theconditions of ion implantation, or the like are adjusted such that adoping amount of impurities implanted into the piezoresistive portions71 a, 71 b, 71 c, and 71 d is greater than that implanted into theconnection portions 73 c and 73 d and the wirings 41 a, 41 b, 41 c, and41 d.

For example, in the case where an ion implantation of boron is performedat 17 keV, an ion implanting concentration implanted into thepiezoresistive portions 71 a, 71 b, 71 c, and 71 d is about 1×10¹³atoms/cm² to 1×10¹⁵ atoms/cm², and the ion implanting concentrationimplanted into the connection portions 73 c and 73 d and the wirings 41a, 41 b, 41 c, and 41 d is about 1×10¹⁵ atoms/cm² to 5×10¹⁵ atoms/cm².

-   Inter-Layer Insulation Film•Wiring Layer Forming Processes

Inter-layer insulation films 81A and 83A and the wiring layers 82 and 84are formed on the top surface of the structure member 10B obtained inthe above-described process, as illustrated in FIG. 5D. Accordingly, astructure member 10C is obtained, in which the sensor element 7 and theMOS transistor 87 cover the inter-layer insulation films 81A and 83A andthe wiring layers 82 and 84.

The silicon oxide film is formed by using the sputtering method, the CVDmethod, or the like and the silicon oxide film is patterned by etchingsuch that formation of the inter-layer insulation films 81A and 83A isperformed.

Here, each thickness of the inter-layer insulation films 81A and 83A isnot particularly limited, but, for example, is about 1500 nm to 5000 nm.

In addition, after a layer made of, for example, aluminum is formed onthe inter-layer insulation films 81A and 83A by using the sputteringmethod, the CVD method, or the like, the layer is patterned such thatformation of the wiring layers 82 and 84 is performed.

Here, each thickness of the wiring layers 82 and 84 is not particularlylimited, but, for example, is about 300 nm to 900 nm.

In addition, the wiring layers 82 a and 84 a each have an annular shapeto surround a plurality of sensor elements 7 in a plan view. Inaddition, the wiring layers 82 b and 84 b are electrically connected toa wiring (for example, wiring that configures a part of thesemiconductor circuit 9) formed on and above the semiconductor substrate61.

A stacking structure of such inter-layer insulation films and wiringlayers is formed by using a common CMOS process, and the number ofstacked layers is appropriately set, as necessary. That is, more wiringlayers are stacked through the inter-layer insulation films, asnecessary, in some cases.

Cavity Section Forming Process

After the front surface protective film 85 is formed on the top surfaceof the structure member 10D obtained in the above-described process byusing the sputtering method, the CVD method, or the like, as illustratedin FIG. 6A, the cavity section 5 is formed by etching. Accordingly, astructure member 10D including the cavity section 5 is obtained.

The front surface protective film 85 is configured to have a pluralityof film layers containing one or more types of materials and is formedsuch that a fine hole 842 of the covering layer 841 is not sealed.Examples of constituent materials of the front surface protective film85 include a silicon oxide film, a silicon nitride film, a polyimidefilm, an epoxy resin film, or the like, which has resistance againstmoisture, dust, a defect, or the like so as to protect the element.

Here, the thickness of the front surface protective film 85 is notparticularly limited, but, for example, is about 500 nm to 2000 nm.

In addition, apart of the inter-layer insulation films 83A and 85A isremoved by etching through a plurality of fine holes 842 formed in thecovering layer 841 such that formation of the cavity section 5 isperformed. Here, in the case where wet etching is used as such etching,an etchant of hydrofluoric acid, buffered hydrofluoric acid, or the likeis supplied from the plurality of fine holes 842, and in the case wheredry etching is used, an etching gas of hydrofluoric acid gas, or thelike is supplied from the plurality of fine holes 842.

Sealing Process

Next, the sealing layer 86 that is made of a silicon oxide film, asilicon nitride film, a metal film such as AL, Cu, W, Ti, TiN, or thelike is formed on the covering layer 841 by using the sputtering method,the CVD method, or the like, as illustrated in FIG. 6B, and then eachfine hole 842 is sealed. Accordingly, a structure member 10E isobtained, in which the cavity section 5 is sealed by the sealing layer86.

Here, the thickness of the sealing layer 86 is not particularly limited,and, for example, is about 1000 nm to 5000 nm.

Diaphragm Forming Process

Finally, the underside of the semiconductor substrate 61A is ground, anda semiconductor substrate 61B that is thin throughout is obtained asillustrated in FIG. 6C. Then, a part of the underside of thesemiconductor substrate 61B is further removed, for example, by dryetching as illustrated in FIG. 6D. Accordingly, the physical quantitysensor 1 is obtained, in which the diaphragm section 64 that is thinnerthan the periphery, is formed.

Here, a reduction in the thickness of the semiconductor substrate 61A bygrinding is not particularly limited, but, for example, is about 100 μmto 400 μm.

In addition, when a part of the underside of the semiconductor substrate61B is removed, the silicon oxide film 62 functions as an etching stoplayer. Accordingly, it is possible to regulate the thickness of thediaphragm section 64 with high accuracy.

The method of removing a part of the underside of the semiconductorsubstrate 61B is not limited to dry etching, and may be wet etching orthe like. In addition, in a case where the diaphragm section 64 includesa part of the semiconductor substrate 61, the thickness of thesemiconductor substrate 61 in the portion may be about 80 μm or less.

It is possible to manufacture the physical quantity sensor 1 throughsuch processes. It is possible to fabricate an active element other thanthe MOS transistor 87, and circuit components such as a capacitor, aninductor, a resistor, a diode, and a wiring that are included in thesemiconductor circuit 9 during an appropriate process described above(for example, the vibration element forming process, the insulation filmforming process, the covering layer forming process, or the sealinglayer forming process). For example, it is possible to form aninter-circuit element separating film along with the silicon oxide film62, to form the gate electrode, a capacitor electrode, a wiring, or thelike along with the sensor element 7, to form the gate insulating film,a capacitor dielectric layer, and the inter-layer insulation film alongwith the inter-layer insulation films 81 and 83, and to form anintra-circuit wiring along with the wiring layers 82 and 84.

Second Embodiment

Next, a second embodiment of the physical quantity sensor according tothe invention will be described.

FIG. 7 is a cross-sectional view illustrating the second embodiment ofthe physical quantity sensor according to the invention.

Hereinafter, the second embodiment of the physical quantity sensoraccording to the invention will be described, but differences from theabove-described embodiment are focused on and described, and thedescriptions of the same details are not repeated.

The second embodiment is the same as the above-described firstembodiment except for the configuration of the diaphragm section.

A diaphragm section 64A that is included in a physical quantity sensor1A illustrated in FIG. 7 is configured to have the silicon nitride film63. The diaphragm section 64A is formed by providing a concave section65A that penetrates the semiconductor substrate 61 and the silicon oxidefilm 62 on the underside of the substrate 6. In the diaphragm section64A, the underside of the silicon nitride film 63 is a pressurereceiving surface 641A.

The silicon nitride film 63 has a lower etching rate with respect to thealkali etchant than silicon. Thus, when the semiconductor substrate 61is etched by using the alkali etchant from the side opposite to theelement-periphery structure member 8, and forms the diaphragm section64A, it is possible to use the silicon nitride film 63 as the etchingstop layer.

In addition, the diaphragm section 64A is configured to have only thesilicon nitride film 63, and thus it is possible to realize theextremely thin diaphragm section 64A.

It is possible to achieve the low profile and to lower the cost also byapplying the physical quantity sensor 1A as described above.

Third Embodiment

Next, a third embodiment of a physical quantity sensor according to theinvention will be described.

FIG. 8 is a cross-sectional view illustrating the third embodiment ofthe physical quantity sensor according to the invention.

Hereinafter, the third embodiment of the physical quantity sensoraccording to the invention will be described, but differences from theabove-described embodiment are focused on and described, and thedescriptions of the same details are not repeated.

The third embodiment is the same as the above-described first embodimentexcept for the configuration of the diaphragm section.

A diaphragm section 64B that is included in a physical quantity sensor1B illustrated in FIG. 8 is configured to have the silicon nitride film63 and a metal film 67.

The metal film 67 is disposed between the silicon oxide film 62 and thesilicon nitride film 63. A part of the silicon oxide film 62 may be leftout in the vicinity of the diaphragm section 64B. In this case, themetal film 67 is to be disposed between the semiconductor substrate 61and the silicon nitride film 63.

The diaphragm section 64B is formed by providing a concave section 65Bthat penetrates the semiconductor substrate 61 and the silicon oxidefilm 62 on the underside of the substrate 6B in which the semiconductorsubstrate 61, the silicon oxide film 62, the metal film 67, and thesilicon nitride film 63 are stacked in the above order. In the diaphragmsection 64B, the underside of the metal film 67 is a pressure receivingsurface 641B.

The metal film 67 has a lower etching rate with respect to the alkalietchant than silicon. Thus, when the semiconductor substrate 61B isetched by using the alkali etchant from the side opposite to theelement-periphery structure member 8, and forms the diaphragm section64B, it is possible to use the metal film 67 as the etching stop layer.

In addition, the diaphragm section 64B is configured to have the siliconnitride film 63 and the metal film 67, and thus it is possible torealize the extremely thin diaphragm section 64B.

In addition, since the metal film 67 has good conductivity, it ispossible to use the metal film 67 as a grounding link.

Constituent materials of such a metal film 67 are not particularlylimited, and it is possible to use various metal materials. However, itis preferable that a wiring material such as aluminum or copper be usedin terms of affinity with the CMOS process. In addition, in terms of agood mechanical characteristics of the diaphragm section 64B, as theconstituent materials of the metal film 67, it is possible to use asuperelastic alloy such as a Ni—Ti alloy, a Cu—Zn alloy, a Ni—Al alloy,a Cu—Cd alloy, a Au—Cd alloy, a Au—Cd—Ag alloy, or a Ti—Al—V alloy, ashape memory alloy, or a relatively high elastic material.

It is possible to achieve the low profile and to lower the cost also byapplying the physical quantity sensor 1B as described above.

2. Pressure Sensor

Next, a pressure sensor (pressure sensor according to the invention)which includes the physical quantity sensor according to the inventionwill be described. FIG. 9 is a cross-sectional view illustrating anexample of the pressure sensor according to the invention.

As illustrated in FIG. 9, a pressure sensor 100 according to theinvention includes the physical quantity sensor 1, a housing 101 thataccommodates the physical quantity sensor 1, and a computation unit 102that computes a signal obtained from the physical quantity sensor 1 intopressure data. The physical quantity sensor 1 is electrically connectedto the computation unit 102 through a wire 103.

The physical quantity sensor 1 is fixed on the inner side of the housing101 by using fixing means not illustrated. In addition, in the housing101, the diaphragm section 64 of the physical quantity sensor 1 has athrough-hole 104 for communicating with the atmosphere (outer side ofthe housing 101).

In such a pressure sensor 100, the diaphragm section 64 receivespressure through the through-hole 104. The signal of the receivedpressure is transmitted to the computation unit through the wire 103 andis computed into the pressure data. The computed pressure data can bedisplayed through a display unit not illustrated (for example, a monitorof a personal computer).

3. Altimeter

Next, an example of an altimeter (altimeter according to the invention)that includes the physical quantity sensor according to the inventionwill be described. FIG. 10 is a perspective view illustrating an exampleof the altimeter according to the invention.

An altimeter 200 can be worn on a wrist like a watch. In addition, thephysical quantity sensor 1 (pressure sensor 100) is mounted inside thealtimeter 200, and thus it is possible to display an altitude at acurrent location above sea level, atmospheric pressure at the currentlocation, or the like on a display unit 201.

Various items of information such as current time, a user's heart rate,or climate conditions can be displayed on the display unit 201.

4. Electronic Apparatus

Next, a navigation system will be described, to which an electronicapparatus including the physical quantity sensor according to theinvention is applied. FIG. 11 is a front view illustrating an example ofthe electronic apparatus according to the invention.

A navigation system 300 includes a position information acquiring unitusing map information not illustrated and a Global Positioning System(GPS), a self-contained navigation unit using a gyro sensor and anacceleration sensor and vehicle speed data, the physical quantity sensor1, and a display unit 301 that displays predetermined positioninformation or course information.

In the navigation system, it is possible to acquire altitude informationin addition to the acquired position information. Acquisition of thealtitude information makes it possible to distinguish an elevated roadfrom a general road. For example, in the case of travelling on theelevated road displayed substantially at the same position as thegeneral road on the position information without the altitudeinformation, it is not possible to be determined in the navigationsystem whether travelling occurs on the general road or on the elevatedroad and information on the general road is provided to a user aspriority information. However, in the navigation system 300 according tothe embodiment, the altitude information can be acquired by the physicalquantity sensor 1, an altitude change is detected by approaching theelevated road from the general road, and it is possible to provide thenavigation information on a state of travelling on the elevated road tothe user.

The display unit 301 is configured to be capable of being miniaturizedand thinned by using a liquid crystal panel display, organicelectro-luminescence (EL) display, or the like.

The electronic apparatus including the physical quantity sensoraccording to the invention is not limited thereto, but can be appliedto, for example, a personal computer, a mobile phone, a medicalapparatus (for example, an electronic thermometer, a sphygmomanometer, ablood glucose meter, an electrocardiogram measuring device, anultrasonic diagnostic apparatus, or an electronic endoscope), variousmeasurement apparatuses, meters (for example, meters in a vehicle, anaircraft, or a ship), or a flight simulator.

5. Moving Object

Next, a moving object (moving object according to the invention) towhich the physical quantity sensor according to the invention is appliedwill be described. FIG. 12 is a perspective view illustrating an exampleof the moving object according to the invention.

As illustrated in FIG. 12, a moving object 400 includes a vehicle body401 and four wheels 402, and is configured such that a drive source(engine) (not illustrated) provided in the vehicle body 401 causes thewheels 402 to rotate. The navigation system 300 (physical quantitysensor 1) is built into such a moving object 400.

As above, the physical quantity sensor, the pressure sensor, thealtimeter, the electronic apparatus, and the moving object according tothe invention are described in accordance with each embodimentillustrated in the drawings, but the invention is not limited thereto,and a configuration of each component can be substituted with anarbitrary configuration that has a similar function. In addition, otherarbitrary constituent objects or processes may be added thereto.

In addition, in the above-described embodiments, a case of using thepiezoresistive element as the sensor element is described as an example,but the invention is not limited thereto. For example, it is possible touse the vibration element such as a flap type vibrator, and other MEMSvibrators such as a comb electrode, or a quartz crystal vibrator.

In addition, in the above-described embodiment, the case of using foursensor elements is described as an example, but the invention is notlimited thereto. The number of the sensor elements may be one to three,or five or more.

In addition, in the above-described embodiment, a case of disposing thesensor element on the surface opposite to the pressure receiving surfaceof the diaphragm section is described as an example, but the inventionis not limited thereto. The sensor element may be disposed on thepressure receiving surface of the diaphragm section, or on both surfacesof the diaphragm section.

In addition, in the above-described embodiment, a case of disposing thesensor element on the outer circumference side of the diaphragm sectionis described as an example, but the invention is not limited thereto.The sensor element may be disposed at the center portion of thediaphragm section.

What is claimed is:
 1. A physical quantity sensor comprising: asemiconductor substrate; a diaphragm section that is disposed above thesemiconductor substrate and does not include the semiconductor substrateand is flexurally deformed when receiving pressure; a plurality ofsensor elements that are formed on a top surface of the diaphragmsection; a wall section that is disposed above one surface side of thesemiconductor substrate and configures a cavity together with thediaphragm section; and a circuit section that is provided above the samesurface side as the wall section of the semiconductor substrate, whereinthe wall section includes an inter-layer insulation film formed on awiring layer of the circuit section, and wherein the inter-layerinsulation film has an annular shape to surround the plurality of sensorelements in a plan view.
 2. The physical quantity sensor according toclaim 1, wherein the sensor element has a piezoresistive element.
 3. Thephysical quantity sensor according to claim 1, wherein the sensorelement is disposed above the same surface side as the wall section ofthe diaphragm section.
 4. The physical quantity sensor according toclaim 1, wherein the circuit section has an insulation layer that isdisposed above the semiconductor substrate and a wiring section thatpenetrates through the insulation layer, and wherein the wall section isformed through the same film formation as at least one of the insulationlayer and the wiring section.
 5. The physical quantity sensor accordingto claim 4, wherein the diaphragm section includes a layer that isconfigured of a material which has a lower etching rate with respect toan acid etchant than the insulation layer.
 6. The physical quantitysensor according to claim 1, wherein the diaphragm section includes alayer that is configured of a material which has a lower etching ratewith respect to an alkali etchant than the semiconductor substrate. 7.The physical quantity sensor according to claim 1, wherein the diaphragmsection includes at least one film of a silicon oxide film, a siliconnitride film, and a metal film.
 8. The physical quantity sensoraccording to claim 1, wherein the inside of the cavity is depressurizedto be below atmospheric pressure.
 9. A pressure sensor comprising: thephysical quantity sensor according to claim
 1. 10. An altimetercomprising: the physical quantity sensor according to claim
 1. 11. Anelectronic apparatus comprising: the physical quantity sensor accordingto claim
 1. 12. A moving object comprising: the physical quantity sensoraccording to claim 1.